NEW METHODS FOR ULTRASONIC NDE OF DIFFICULT MATERIALS

在许多工程应用中，采用表现出异质或以其他方式声散射微观结构的材料，示例包括奥氏体钢和合金、混凝土和纤维增强复合材料。在这种高散射介质的超声无损评价（NDE）中，缺陷目标信号经常被杂波回波所掩盖，杂波回波是由许多相对较小（相对于超声波长）的固定反射体引起的，这些反射体形成材料内部微结构的一部分。这种杂乱的程度可能是显著的，甚至比这些随机散射区域更大的缺陷也可能难以检测。这种类型的时不变杂波噪声不能通过用于减少时变随机电噪声的标准时间平均或相关技术来减少。因此，缺陷识别总是涉及可实现的分辨率（其部分地由材料中的波长确定）与由传播介质中的散射引起的噪声之间的折衷。本计画将探讨一系列改善难加工材料超音波无损检测之方法。该方法将涉及超声波束建模，新颖的换能器设计和阵列信号处理方法的组合。

In many engineering applications, materials that exhibit heterogeneous or otherwise acoustically scattering microstructure are employed, examples include austenitic steels and alloys, concrete and fibre reinforced composites. In ultrasonic non destructive evaluation (NDE) of such highly scattering media, the defect target signal is frequently obscured by clutter echoes, caused by numerous, relatively small (relative to the ultrasonic wavelengths), stationary reflectors, which form part of the internal microstructure of the material. The extent of this clutter can be significant and even defects that are larger than these randomly scattering regions can be difficult to detect. This type of time-invariant clutter noise cannot be reduced by the standard time averaging or correlation techniques that are used to reduce time varying random electrical noise. Accordingly, defect identification invariably involves a compromise between achievable resolution, which is determined partly by wavelength in the material, and the noise arising from scattering in the propagation medium. This project will investigate a range of methods for improved ultrasonic NDE of difficult materials. The approach will involve a combination of ultrasonic beam modelling, novel transducer design and array signal processing methods.